This invention provides wire-coated ion bombarded graphite field emission electron emitters, a process for producing them and their use in field emitter cathodes in flat panel display screens.
Field emission electron sources, often referred to as field emission materials or field emitters, can be used in a variety of electronic applications, e.g., vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers and klystrons and in lighting.
Display screens are used in a wide variety of applications such as home and commercial televisions, laptop and desktop computers and indoor and outdoor advertising and information presentations. Flat panel displays are only a few inches thick in contrast to the deep cathode ray tube monitors found on most televisions and desktop computers. Flat panel displays are a necessity for laptop computers, but also provide advantages in weight and size for many of the other applications. Currently laptop computer flat panel displays use liquid crystals which can be switched from a transparent state to an opaque one by the application of small electrical signals. It is difficult to reliably produce these displays in sizes larger than that suitable for laptop computers or for operation over a wide temperature range.
Plasma displays have been used as an alternative to liquid crystal displays. A plasma display uses tiny pixel cells of electrically charged gases to produce an image and requires relatively high electrical power to operate.
Flat panel displays having a cathode using a field emission electron source, i.e., a field emission material or field emitter, and a phosphor capable of emitting light upon bombardment by electrons emitted by the field emitter have been proposed. Such displays have the potential for providing the visual display advantages of the conventional cathode ray tube and the depth and weight advantages of the other flat panel displays with the additional advantage of lower power consumption than the other flat panel displays.
U.S. Pat. Nos. 4,857,799 and 5,015,912 disclose matrix-addressed flat panel displays using micro-tip cathodes constructed of tungsten, molybdenum or silicon. WO 94-15352, WO 94-15350 and WO 94-28571 disclose flat panel displays wherein the cathodes have relatively flat emission surfaces.
WO 97-07524 discloses the advantages that a fibrous cathode has over a relatively flat one.
There is a need for a process for readily and economically producing wire or fiber-like electron emitters for use in fibrous cathodes.
This invention provides a process for producing a wire-coated ion bombarded graphite field emission electron emitter, which comprises:
(a) forming a layer of composite which comprises graphite particles and glass on a wire, wherein the glass adheres to the wire and to portions of the graphite particles thereby affixing the graphite particles to one another and to the wire, and
(b) bombarding the surface of the layer formed in (a) with an ion beam.
Preferably, at least 50% of the surface area of the layer of composite consists of portions of graphite particles and most preferably, at least 70% of the surface area of the layer of composite consists of portions of graphite particles.
The volume per cent of graphite particles is preferably about 35% to about 80% of the total volume of the graphite particles and the glass, and most preferably about 50% to about 80% of the total volume.
Preferably, the ion beam is an argon ion beam and the argon ion beam has an ion current density of from about 0.1 mA/cm2 to about 1.5 mA/cm2, a beam energy of from about 0.5 keV to about 2.5 keV and the period of ion bombardment is about 15 minutes to about 90 minutes.
Preferably, the glass is a low softening point glass.
Preferably, when the layer of composite comprises graphite and glass, the process for forming the layer of composite on a wire comprises coating the wire with a paste comprised of graphite particles and glass frit and firing the paste. Various methods can be used to coat the wire. For example, the wire can be submersed in or drawn through the paste. Alternatively the paste can be brushed or sprayed onto the wire.
In addition this invention provides a process for forming a layer of composite which comprises graphite and glass on a wire, which comprises:
(a) coating a paste comprised of graphite particles and glass frit onto the wire, wherein the volume per cent of graphite particles is about 35% to about 80% of the total volume of the graphite particles and the glass frit, and
(b) firing the paste to soften the glass frit and cause it to adhere to the wire and to portions of the graphite particles thereby affixing the graphite particles to one another and to the wire to produce the layer of composite, wherein at least 50% of the surface area of the layer of composite consists of portions of graphite particles.
Preferably, at least 70% of the surface area of the layer of composite consists of portions of graphite particles.
In addition this invention provides the layer of composite which comprises graphite and glass on a wire made by the above process and which can be subsequently treated to produce a field emission electron emitter. In the layer of composite which comprises graphite and glass, preferably the volume per cent of graphite particles is about 35% to about 80% of the total volume of the graphite particles and the glass, and most preferably about 50% to about 80% of the total volume.
This invention also provides electron emitters produced by the process of this invention. These electron emitters and the fibrous cathodes made therefrom are useful in vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers, klystrons and lighting devices. The flat panel displays can be planar or curved.